The Rob & Chyna star shocked fans after she took to social media Saturday to debut a small waist a week after giving birth to her and Rob Kardashian‘s daughter Dream Kardashian via C-section, spurring many to speculate she had had weight loss surgery. She set the record straight Sunday.

“So I posted a picture of my belly yesterday and the only reason it got that flat, you guys, is from breastfeeding and breast pumping and from my body already being small before my pregnancy,” Blac Chyna said in a Snapchat video while pumping breast milk.

She revealed on Snapchat Sunday she has lost 21 pounds, recently averaging three in one day, since giving birth 10 days ago to Dream, her and Rob’s first child together and her second overall.

She said in another video posted Sunday that she credits her weight loss to breastfeeding. Mothers who exclusively breastfeed their babies can burn up to 600 calories a day.

“If you are pregnant right now, I would highly recommend breastfeeding and breast pumping, because it’ll get your weight back down fast,” Blac Chyna said on Snapchat.